Ligands
Feedback Mechanisms
Miscellaneous
Cell Cycle
Mitosis
100
In class, we discussed these two classifications of ligands. Also describe how they would bind to a target cell.
1. Hydrophobic - If small enough, can bind inside the cell (probably in the nucleus as a transcription factor).
2. Hydrophilic - Would bind to a receptor protein outside the cell.
100
Name the 2 feedback mechanisms.
What are positive and negative feedback?
100
Give an example of a positive regulator and what it does.
answers will vary.
ex. cdk/cyclin complex - promotes cell cycle to continue via phosphorylation/cascade mechanisms
100
Name the four standard stages of the cell cycle (for a somatic cell).
G1, S, G2, M
100
Name the four stages of mitosis.
What are prophase, metaphase, anaphase and telophase?
200
There are three types of cell junctions. Name them and describe them.
What are gap junctions, tight junctions and adhesion junctions?
200
Describe the two feedback mechanisms found in biology.
positive - a stimulus causes a reaction in the same direction (more response = more signal)
negative - a stimulus causes a reaction in the opposite direction (more response = less signal)
200
Describe how a tumor could form via cell signaling mistakes.
answers will vary
overall, cells send signals to each other to grow or die. usually, cells that are overcrowded will naturally go into apoptosis, however, if the cell has signaling mutations in any of its proteins, it can continue to divide out of control.
200
Interphase consists of these three portions of the cell cycle.
What are G1, S and G2?
200
During metaphase, all chromosomes line up at this structure. How many chromosomes will be lined up at this structure.
What is the metaphase plate? 46.
300
Cells receive ligands, which are signaling molecules from other cells, and sometimes themselves. Once a cell receives a signal, it undergoes a 3 step process:
1. Reception
2. Transduction
3. Response
Describe each step.
Reception - Target cells (cells with the matching receptor) will accept the ligand via the receptor protein.
Transduction - Once the ligand bound to the receptor protein, it caused a conformational change in that receptor, which initiates a signaling cascade that involves the activation of multiple proteins/enzymes.
Response - At the end of the signal transduction pathway, a cellular response will be triggered. (the goal of the original ligand)
300
When our blood sugar is high, the pancreas releases insulin, which stimulates glycogen (stored glucose) formation and thus lowers our blood sugar. Type 1 diabetics cannot produce insulin, while type 2 diabetics have mutated insulin that the body no longer responds to. Describe what kind of feedback mechanism this process is utilizing.
This process utilizes a negative feedback mechanism.
High blood sugar results in low blood sugar after release of the signal.
300
Some regulators within a cell will promote or inhibit the cell cycle. How do we classify these regulators?
These are internal regulators.
300
Describe the G0 phase and give an example of cells in this phase.
Three of the four cell cycle stages have checkpoints. Name these stages and what their checkpoints are "looking" for.
The G0 phase is when a cell is not going to actively divide. A cell will go into this phase at some point between the end of M phase and G1, since it would commit to division during the G1 checkpoint. The cell is alive and healthy.
Neurons are a great example.
300
How many chromosomes are present in a mitotic cell during anaphase/telophase?
92
400
Ligands travel various distances. We classify them based on how far they travel to reach a target cell. Name and describe the four classifications.
1. Autocrine - self signaling
2. Juxtacrine - between gap juntions
3. Paracrine - between nearby cells (good ex. neurons)
4. Endocrine - cells at a large distance from one another (ex. hormones via the endocrine system)
400
Childbirth utilizes a positive feedback mechanism. Using the following terms, describe how: oxytocin, uterus, pituitary gland, cervix.
Ones contractions begin, the baby's head is pushed against the cervix. Nerve endings on the cervix send impulses to the brain, which then stimulates the pituitary gland to release oxytocin which travels via endocrine signaling to the uterus, promoting further contractions. The cycle continues until birth occurs.
400
Describe a tyrosine kinase receptor and how it leads to a cellular response when activated.
tyrosine kinases form dimers when bound to the appropriate ligand. This results in the phosphorylation of tyrosine (trading of its -OH group to a phosphorous group). Next, a relay protein is activated and a kinase cascade results. Finally, a cellular response occurs.
400
Three of the four cell cycle stages have checkpoints. Name these stages and what their checkpoints are "looking" for.
G1 - check for healthy, growing cell, organelles, proteins for synthesis, ready for S phase. Cell commits to division here.
G2 - checks all DNA has been properly replicated, checks that chromosomes are ready to be condensed, extra organelles/cytoplasm for division.
M - during metaphase, checks all chromosomes are correctly aligned on metaphase plate so that there is no unequal distribution between daughter cells.
400
Describe three important steps that must occur during prophase.
the nucleus/nucleolus must disappear
condensed chromatin --> chromosomes
centrosomes move to polar ends of the cell
spindle fibers attach to chromosomes
500
We consider ligands to be external regulators for the cell cycle. Explain this observation and provide an example.
Ligands have the ability to cause change to a cell's cycle depending on what their message is. Sometimes, ligands send messages for apoptosis or growth.
Ex. HGH - promotes cell growth
500
Come to the board and explain (like a professor) how this promotes homeostasis... your classmates will decide...
answers will vary
500
Describe the p53/p21 cellular regulation mechanism.
p53 is a negative regulator that halts the cell cycle when damaged DNA is detected. It then activates p21 which further halts the cell cycle by deactivating active cdk/cyclin complexes. This mechanism mostly acts during the G1 phase.
500
Describe the two interpretations of the word "cytokinesis" and why its timing in the cell cycle is debated.
cytokinesis - cell movement. this would imply it is its own step after telophase once the daughter cells move apart.
cytokinesis - cytoplasm splitting. this would imply it is part of both anaphase and telophase.
500
Name and describe the different forms of DNA throughout the cell cycle.
How do we count chromosomes in the cell?
chromatin, chromosomes (2 kinds), sister chromatids, homologous chromosomes
based on the number of centromeres